Exemplary embodiments of the present invention relate to a technology for improving the reliability of a nonvolatile memory device.
A memory device is categorized into a volatile memory device and a nonvolatile memory device, depending on whether data is retained when power is interrupted. The volatile memory device is a memory device which loses data when power is interrupted. Examples of the volatile memory device include DRAMs and SRAMs. The nonvolatile memory device is a memory device which retains stored data even though power is interrupted. Examples of the nonvolatile memory device include a flash memory device.
The main operations of the nonvolatile memory device are an erasure operation, a read operation, and a program operation. When the erasure operation and the program operation are repetitively performed on the nonvolatile memory device, the physical characteristics of the nonvolatile memory device are degraded and the reliability of the memory cells decreases.
Therefore, a technology which selects a memory cell on which an erasure operation and a program operation are repeated among memory cells of the nonvolatile memory device, and manages the degraded memory cell not to be used is useful.